export default {
  bind(el, binding, vnode) {
      const enableDrag = vnode.data.attrs.enableDrag
      if (enableDrag) {
          const dialogHeaderEl = el.querySelector('.el-dialog__header')
          const dragDom = el.querySelector('.el-dialog')
          dialogHeaderEl.style.cssText += ';cursor:move;'
          dragDom.style.cssText += ';top:0px;'

          // 获取原有属性 ie dom元素.currentStyle 火狐谷歌 window.getComputedStyle(dom元素, null);
          const getStyle = (function() {
              if (window.document.currentStyle) {
                  return (dom, attr) => dom.currentStyle[attr]
              } else {
                  return (dom, attr) => getComputedStyle(dom, false)[attr]
              }
          })()

          dialogHeaderEl.onmousedown = (e) => {
              // 鼠标按下，计算当前元素距离可视区的距离
              const disX = e.clientX - dialogHeaderEl.offsetLeft
              const disY = e.clientY - dialogHeaderEl.offsetTop

              const dragDomWidth = dragDom.offsetWidth
              const dragDomHeight = dragDom.offsetHeight

              const screenWidth = document.body.clientWidth
              const screenHeight = document.body.clientHeight

              const minDragDomLeft = dragDom.offsetLeft
              const maxDragDomLeft = screenWidth - dragDom.offsetLeft - dragDomWidth

              const minDragDomTop = dragDom.offsetTop
              const maxDragDomTop = screenHeight - dragDom.offsetTop - dragDomHeight

              // 获取到的值带px 正则匹配替换
              let styL = getStyle(dragDom, 'left')
              let styT = getStyle(dragDom, 'top')

              if (styL.includes('%')) {
                  styL = +document.body.clientWidth * (+styL.replace(/\%/g, '') / 100)
                  styT = +document.body.clientHeight * (+styT.replace(/\%/g, '') / 100)
              } else {
                  styL = +styL.replace(/\px/g, '')
                  styT = +styT.replace(/\px/g, '')
              }

              document.onmousemove = function(e) {
                  // 通过事件委托，计算移动的距离
                  let left = e.clientX - disX
                  let top = e.clientY - disY

                  // 边界处理
                  if (-(left) > minDragDomLeft) {
                      left = -minDragDomLeft
                  } else if (left > maxDragDomLeft) {
                      left = maxDragDomLeft
                  }

                  if (-(top) > minDragDomTop) {
                      top = -minDragDomTop
                  } else if (top > maxDragDomTop) {
                      top = maxDragDomTop
                  }

                  // 移动当前元素
                  dragDom.style.cssText += `;left:${left + styL}px;top:${top + styT}px;`
                  // emit onDrag event
                  vnode.child.$emit('dragDialog')
              }

              document.onmouseup = function(e) {
                  document.onmousemove = null
                  document.onmouseup = null
              }
          }
      }
  }
}
